This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2017-170224 filed on Sep. 5, 2017, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a fixing device, and to an image forming apparatus provided with a fixing device. More particularly, the present disclosure relates to a fixing device having a static elimination sheet for eliminating electrical charge from the surface of a pressing member, and to an image forming apparatus provided with such a fixing device.
Conventionally, image forming apparatuses are provided with a fixing device for fixing a toner image transferred to a recording medium such as a sheet or the like from an image carrying member. As fixing devices, there are known those adopting a roller fixing method provided with a heating roller and a pressing roller rotating while in contact with each other, and those adopting a belt fixing method using an endless fixing belt as a heating member. For example, a fixing device of a roller fixing method heats and presses a toner image carried on a sheet in a nip portion between a fixing roller and a pressing roller kept in pressed contact with each other, and thereby fixes the toner image on the sheet.
In this fixing device, a pressing roller generally used is provided with an elastic layer of silicone rubber or the like on the circumference of a metal core and the circumference is further provided with a release layer of fluorine resin or the like. These elastic and release layers are electrically insulating, and thus the surface of the pressing roller can be charged to minus several thousand volts by friction with a recording medium. This can cause the recording medium to wind around the pressing roller and toner to attach to the fixing roller.
To avoid that, an image forming apparatus is proposed in which a fixing housing and a conveying guide of resin arranged around the pressing roller are provided with a static elimination sheet extending in the axial direction of the pressing roller, and in which the static elimination sheet is electrically grounded to the main body of the image forming apparatus via a plate spring.
According to one aspect of the present disclosure, a fixing device includes a heating member, a pressing member, a pressurizing mechanism, and a pressing force changing mechanism. The heating member heats an unfixed toner image carried on a recording medium. The pressing member forms a fixing nip portion by making contact with the heating member. The pressurizing mechanism presses the pressing member against the heating member. The pressing force changing mechanism changes the pressing force of the pressing member against the heating member. The fixing device fixes the unfixed toner image to the recording medium passing through the fixing nip portion. The pressing force changing mechanism has an electrically conductive rotation shaft arranged parallel to the pressing member and opposite the surface of the pressing member across a predetermined interval, and a pressing force changing member provided at an end part of the rotation shaft and rotating about the rotation shaft to change the pressing force of the pressurizing mechanism. The rotation shaft is electrically grounded. The rotation shaft is provided with a static elimination sheet for eliminating electrical charge from the surface of the pressing member.
Further features and advantages of the present disclosure will become apparent from the description of embodiments given below.
Hereinafter, with reference to the accompanying drawings, an embodiment of the present disclosure will be described.
With reference to
In the image forming section P, a photosensitive drum (image carrying member) 2 carrying a visible image (toner image) is arranged. The toner image formed on the photosensitive drum 2 is transferred to a recording medium 6 such as regular paper, an envelope, or thick paper, and is then fixed to the recording medium 6 in a fixing device 30. Then, the recording medium 6 is discharged from an apparatus main body. While the photosensitive drum 2 is rotated by an unillustrated drum driving motor in the clockwise direction in
Around and in front of (on the right side in
The recording medium 6 having a toner image transferred to it by the photosensitive drum 2 is conveyed to the fixing device 30. The recording medium 6 conveyed to the fixing device 30 is heated and pressed by a fixing roller 31 and a pressing roller 32 described later, so that the toner image is fixed to the surface of the recording medium 6, and thereby a predetermined image is formed. The recording medium 6 having passed through the fixing device 30 is curled. Thus, on the downstream side of the fixing device 30 in the recording medium conveying direction, a decurling device 60 (see
As shown in
As the fixing roller 31, what is called a hard roller is used which is a cylindrical metal core made of metal with excellent thermal conductivity such as aluminum or iron coated with a coating or a tube of a fluorine resin. Inside the metal core of the fixing roller 31, a halogen heater 33 is provided as a heat source, so that the surface of the fixing roller 31 is kept at a predetermined temperature. Used as the pressing roller 32 is a cylindrical base made of synthetic resin, metal, or other material having formed on it an elastic layer of silicone rubber or the like. The elastic layer is covered on its surface with a release layer with excellent mold releasability such as fluorine resin or the like.
The fixing roller 31 is rotatably held on a fixing frame (unillustrated). The pressing roller 32 has both end parts of a rotation shaft 32a rotatably held on a pair of bearing members 34. As shown in
As shown in
The pressing force changing mechanism 50 includes an eccentric cam 51 in which the distance from the rotation center to the circumferential face varies in the circumferential direction, and a driving source (unillustrated) which rotates a rotation shaft 51a of the eccentric cam 51. The eccentric cam 51 is provided approximately symmetrically at either side of the fixing device 30 in its longitudinal direction, and is fixed at both end parts of one rotation shaft 51a. The eccentric cam 51 has a small-diameter part 51b in which the distance from the rotation center to the circumferential face is shortest, a maximum-diameter part 51d in which the distance from the rotation center to the circumferential face is longest, and a large-diameter part 51c in which the distance from the rotation center to the circumferential face is longer than that in the small-diameter part 51b but shorter than that in the maximum-diameter part 51d.
When the small-diameter part 51b of the eccentric cam 51 is in contact with the contact piece 41b of the pressurizing lever 41 (the state in
On the other hand, when, as shown in
When the maximum-diameter part 51d is put into contact with the contact piece 41b, the pressing force of the pressing roller 32 against the fixing roller 31 increases further.
The rotation shaft 51a of the eccentric cam 51 is arranged parallel to the pressing roller 32, and is arranged opposite the surface of the pressing roller 32 across a predetermined interval (here, about 5 mm). The rotation shaft 51a is, in both end parts, rotatably pivoted on the guide members 36 (see
As shown in
As shown in
The static elimination sheet 37 is an electrically conductive sheet-form member, such as a sheet of nonwoven, woven, or knit fabric coated with conductive polymer, or a sheet mixed with metal fiber or carbon fiber.
As shown in
The pressing roller 61 has both end parts of a rotation shaft 61a rotatably held on a pair of bearing members (unillustrated), and is biased by a pair of a biasing member 63 comprising a compression spring provided in the decurling device 60 in a direction approaching the correcting roller 62. The biasing member 63 is arranged at either side of the pressing roller 61.
The holding member 71 is configured to be swingable, about a swinging shaft 71a provided in a lower end part of it, in such directions as to make the correcting roller 62 approach and recede from the pressing roller 61.
The holding member 71 is biased by the biasing member 72 in the leftward direction in
In this image forming apparatus 1, when an image is formed on regular paper, as shown in
On the other hand, for example, when an image is formed on an envelope, to suppress winkles on the envelope, as shown in
Here, the pressing roller 32 moves a small distance (about 1 to 2 mm) approximately linearly in the direction (the rightward direction in
In this embodiment, as described above, the rotation shaft 51a which is arranged opposite the surface of the pressing roller 32 across a predetermined interval is provided with the static elimination sheet 37 for eliminating electrical charge from the surface of the pressing roller 32. Thus, it is possible to suppress charging of the pressing roller 32, and thus, it is also possible to suppress winding of the recording medium 6 around the pressing roller 32 and attachment of toner to the fixing roller 31.
Providing the rotation shaft 51a with the static elimination sheet 37 permits the static elimination sheet 37 to be electrically grounded via the rotation shaft 51a. Thus, it is not necessary to additionally provide a plate spring or the like as in conventional image forming apparatuses, and thus it is not necessary to increase the number of components and to secure a space for arrangement of a plate spring. It is possible to reduce manufacturing cost and weight compared with when a fixing housing and a conveying guide (neither is shown) are made of metal and a static elimination sheet 37 is arranged on them.
As described above, in the fixing device 30 in which the pressing force of the pressing roller 32 against the fixing roller 31 can be changed, it is possible to eliminate electrical charge from the surface of the pressing roller 32 with a simple structure.
As described above, the static elimination sheet 37 is helically wound around the rotation shaft 51a. Thus, it is possible to effectively suppress the peeling off of the static elimination sheet 37 from the rotation shaft 51a. The temperature of the fixing device 30 becomes high, and this causes the static elimination sheet 37 to peel off easily. Thus, it is particularly effective that the static elimination sheet 37 is helically wound around the rotation shaft 51a to suppress the peeling off of the static elimination sheet 37 from the rotation shaft 51a.
As described above, the rotation shaft 51a is arranged near a line L2 which passes through the center O32 of the pressing roller 32 and which is perpendicular to a line L1 connecting between the center O31 of the fixing roller 31 and the center O32 of the pressing roller 32. Thus, even when the pressing roller 32 is moved a small distance to the right side so as to be in a reduced pressure state, the distance from the surface of the pressing roller 32 to the static elimination sheet 37 hardly changes, and thus it is possible to easily suppress complicating the elimination of electrical charge from the surface electrical charge of the pressing roller 32.
As described above, the center O51 of the rotation shaft 51a is arranged within an angle range R of 20 degrees or less about the center O32 of the pressing roller 32 with respect to the line L2. Thus, even when the pressing roller 32 is moved a small distance to the right side so as to be in a reduced pressure state, it is possible to sufficiently suppress complicating the elimination of electrical charge from the surface electrical charge of the pressing roller 32.
As described above, the pressurizing mechanism 40 is pivotable about the swing shaft 41a and has the pressurizing lever 41 pressing the pressing roller 32 against the fixing roller 31. The eccentric cam 51 presses the pressurizing lever 41 in the predetermined direction. Thus, by rotating the eccentric cam 51 about the rotation shaft 51a, it is possible to change the pressing force of the pressurizing mechanism 40 easily.
As described above, the fixing device 30 has the biasing member 35 biasing the pressurizing lever 41 in the direction opposite to the direction in which the eccentric cam 51 presses the pressing lever 41. Thus, it is possible to easily pivot the pressurizing lever 41 in the clockwise direction or the counter-clockwise direction in coordination with the rotating of the eccentric cam 51.
The embodiments disclosed herein should be understood to be in every respect illustrative and not restrictive. The scope of the present disclosure is not defined by the description of embodiments given above but by the appended claims, and encompasses any modifications made in the sense and scope equivalent to those of the claims.
For example, although the embodiments described above deal with an example where the present disclosure is applied to a monochrome printer, this is not meant to limit the present disclosure. Needless to say, the present disclosure find applications in a variety of image forming apparatuses provided with a fixing device, such as color printers, monochrome copiers, digital multifunction peripherals and facsimile machines.
Although the embodiments described above deal with an example where the pressurizing mechanism 40 serves also as the pressing force changing mechanism 50, this is not meant to limit the present disclosure. The pressurizing mechanism 40 may not necessarily serve also as the pressing force changing mechanism 50. For example, it may be configured like the fixing device 30 of a first modified example according to the present disclosure shown in
Although the embodiments described above deal with an example where the eccentric cam 51 rotating to change the pressing force of the pressurizing mechanism 40 is provided and the rotation shaft 51a of the eccentric cam 51 is provided with the static elimination sheet 37, this is not meant to limit the present disclosure. For example, the rotation shaft 51a may be provided with a gear (pressing force changing member) so that, as the gear rotates about the rotation shaft 51a, the pressurizing lever pivots via another member (such as a gear train). Then, the rotation shaft 51a of the gear may be provided with the static elimination sheet 37.
Although the embodiments described above deal with an example where the pressing roller 32 moves approximately linearly in the direction away from the fixing roller 31, this is not meant to limit the present disclosure. The pressing roller 32 may be configured to move about a predetermined swinging shaft in the direction away from the fixing roller 31. In that case, for example, it may be configured like a fixing device of a second modified example according to the present disclosure shown in
The technical scope of the present disclosure includes any configuration obtained by appropriately combining the configurations of the embodiments and of the modified examples described above.
Number | Date | Country | Kind |
---|---|---|---|
2017-170224 | Sep 2017 | JP | national |